A network interface protocol defined by CCITT Recommendation I.122 as a packet mode service. In effect it combines the statistical multiplexing and port sharing of X.25 packed switching with the high speed and low delay of time division multiplexing and circuit switching.

Unlike X.25, frame relay implements no layer 3 protocols and only the so-called core layer 2 functions. It is a high-speed switching technology that achieves ten times the packet throughput of existing X.25 networks by eliminating two-thirds of the X.25 protocol complexity. The basic units of information transferred are variable-length frames, using only two bytes for header information. Delay for frame relay is lower than X.25, but it is variable and larger than that experienced in circuit-switched networks.